Throughout 2011, Firefox users have seen their browser's major version number go up very 6 weeks or so, something that was unheard of, in the years before, when it could take years for a major version number increase. Mozilla was obviously inflating version numbers for better market placement with other browsers that have crossed version 9x (such as Chrome, MSIE, and Opera). With Firefox already at version 11, Mozilla wants to slow down with the version number game, which caused "update fatigue" among users. Apart from keeping track of their browser's version number, users that have important add-ons installed, stay away from updates because major version number changes break the add-ons.

Mozilla wants to counter update fatigue with a two pronged approach. Firstly, it will change the way browser version numbers affect add-on compatibility. With Firefox 11, any add-on that's compatible with Firefox 4+ will just run, without compatibility issues. Add-ons disabled by older versions of the browser will now resume working. Next up, Mozilla will introduce completely silent updates, which get downloaded in the background, and don't notify you about restarting the browser to apply updates. You'll never notice when your Firefox reaches version 9001.

I hope silent updates will at least include notification like "Your Firefox has just updated to version X". So you'd know it has updated. Other than that, i don't mind it since i update it regularly anyway.

It was about time they fixed extensions. They jumped the Chrome version numbering bandwagon not taking into account their addons system which isn't like the one in Chrome.
Now i'm just waiting for them to make the damn 64bit version... I know there is Waterfox but no one really supports (specifically avast!'s additional features for browsers) it because it's not widely used.

Next up, Mozilla will introduce completely silent updates, which get downloaded in the background, and don't notify you about restarting the browser to apply updates. You'll never notice when your Firefox reaches version 9001.